This invention relates in general to pulse compressors and relates more particularly to an optical system that can expand and compress optical pulses while substantially retaining the temporal profile of the pulse.
In the figures, the first digit of a reference numeral indicates the first figure in which is presented the element indicated by that reference numeral.
In a conventional optical pulse compressor like that illustrated in FIG. 1, a frequency sweep is imparted to a travelling wave pulse of light by a phase modulation mechanism so that the frequency at the trailing end of the pulse is higher or lower than at the leading end of the pulse. This swept frequency process is referred to as a "chirp" because an audio pulse of comparable shape sounds like the chirp of a bird. When this pulse is transmitted through a dispersive optical element in which the frequency components at the leading edge of the pulse travel slower than the frequency components at the trailing edge of the pulse, the trailing end of the pulse compresses toward the leading edge of the pulse producing a pulse of reduced width and increased amplitude.
In one class of embodiments of such pulse compressors, the frequency chirp is imparted to the input pulse by self-phase modulation in an optical fiber (see, for example, D. Grischkowsky and A. C. Balant, Appl. Phys. Lett. 41, 1 (1982)). In another class of embodiments, the frequency chirp is imparted by electro-optic phase modulation (see, for example, D. Grischkowsky, Appl. Phys. Lett. 25, 566 (1974); or B. H. Kolner, Appl. Phys. Lett. 52, 1122 (1988)). In either case, a quadratic or nearly quadratic time-varying phase shift across the temporal envelope of the pulse results. After the pulse is chirped, it passes through a dispersive delay line such as a diffraction grating-pair which produces temporal compression of the pulse (See, for example, Edmond B. Treacy, "Optical Pulse Compression With Diffraction Gratings", IEEE Journal of Quantum Electronics, Vol. QE-5, No. 9, September 1969).